Janssen Solar Photograph and Optical Studies. 299 
may be here counted, I have placed on the positive a Rogers’ 
reticule, consisting of very small squares, engine-divided on 
glass, which had been actually used on the sun for a similar 
purpose; and with its aid counted the “grains” in different 
should M. Janssen succeed in future in enlarging his photo- 
graph while retaining his present wonderful definition, that 
nition is as sharp and clear as we have escrl d it. ow,—a 
question evidently to be asked,—is this bad definition something 
in the solar atmosphere or our own? oes it mean a tremen- 
away from the facule as seen on the edge? I believe there 
has been, from telescopic study, a somewhat uncertain recog- 
nition that the photospheric structure differed at different times, 
if once recognized, would be visible to the telescope, if sought, 
granulations varied at different times from solar causes; but with 
the telescope we lack the facility for deliberate comparison of 
one part of the disc with another, we obtain here, since owing 
to the undulations which we do know without doubt, are in our 
own atmosphere, our best vision is but momentary, an — 
we can turn from one part of the sun to compare It with another 
the opportunity is gone. The “omg Eaoereraieg as it is, in 
